This invention relates to frame shaft and drive shaft assemblies, and more specifically, to a combined curved frame shaft and sheath for a flexible drive shaft, for use in low horsepower implements such as lawn trimming tools, brush cutters, and the like, in which the shaft assembly is bent to dispose its tool end at an angle to its power input end and power is transmitted through the assembly by a flexible drive shaft.
Various low-horsepower manual implements such as lawn edgers, brush cutters, and the like are available on the market, in which a tubular frame shaft connects a power head at its upper end to a driven tool at its lower end and in which power is transmitted from the head to the tool by a rotating shaft extending through the frame shaft. When such implements carry a rotating cutter or other tool, it is desirable to dispose the tool axis of rotation at an angle to the axis of the tool head and upper portion of the frame shaft, in order to permit the implement to be carried comfortably by an operator in an erect standing or walking position. Such angular relationship has been provided by bending the lower portion of the frame shaft through a suitable arc, and by transmitting power from the power head to the tool by means of a flexible drive shaft contained in a flexible sheath extending through the frame shaft. Commonly, such sheath is formed of a helically wound tape. The sheath has been held generally concentric with the frame shaft by a series of spaced annular bushings.
This arrangement has not been entirely satisfactory In particular, the flexible sheath does not sufficiently hold the flexible drive shaft against distortion and whipping, which produces vibration and wear. Under some circumstances, the flexible sheath for the drive shaft will fail, so that it becomes unwound or enlarged and no longer constrains the drive shaft for rotation on its axis. This results in failure of that shaft and hence of the implement as a whole. The configuration of the shaft assembly, with a long straight portion and adjoining arcuate portion, has heretofore required the use of a flexible sheath and prevented the use of a rigid sheath.
The present invention overcomes the problems and disadvantages of the prior art and provides a shaft assembly of the desired bent configuration in which the rotating flexible drive shaft is firmly and closely supported throughout its length by a rigid sheath.